Mosquito densonucleosis viruses (densoviruses) are mosquito-specific parvoviruses that are pathogenic for mosquitoes. Our long-term goal is to develop them as molecular biological tools for the investigation and control of mosquito-borne disease. We have developed the Aedes densonucleosis virus (AeDNV) as a transducing vector to express genes of interest in mosquito cells and mosquitoes. We propose to extend this work to improve and refine the versatility of these tools. In the first Specific Aim, seven En hand partially characterized densoviral isolates will be cloned, sequenced and characterized with respect to host range, in vitro and in vivo growth characteristics, pathogenesis and ability to be vertically transmitted. In addition, new field isolates will be sought in Thailand, Mexico, and, Africa from mosquito collections by colleagues working in those areas. New isolates will also be characterized. It is anticipated that there will be a range of phenotypes among the viruses. In the second Specific Aim, the constraints to the variability and compatibility of viral nonstructural proteins, terminal inverted repeats and the noncoding region just inside the right end will be investigated. These studies will establish critical parameters for densoviral vector design, and construction of chimeric viruses. In the third Specific Aim, the molecular determinants of phenotypic differences will be mapped on the viral genome by making chimeric viral genomes and comparing the properties of the resulting viruses to the parental viruses. In the fourth Specific Aim, we will attempt to correlate phenotypic properties of the viruses with the ability of the viruses to persist and spread within mosquito populations and between breeding demes in a vivarium. This should provide valuable data for the eventual use of these viruses to control vector populations and vector-borne disease.